Ti-Al intermetallic compounds are attracting attention as a highly promising material for various applications because they are resistant to heat, acid and wear, and extremely light-weight. Typical applications of Ti-Al intermetallic compounds include outer wall members which are exposed to high temperatures, and various engine components such as turbine components, pistons, and valve systems.
According to a known method for fabricating an article made of a Ti-Al intermetallic compound, a mixture of Ti and Al powders was heated to a temperature of approximately 1,300.degree. C. under high pressure. It is also known to carry out a heat treatment to the thus fabricated article at a lower temperature to remove stress existing in the article. Also is known the so-called self-propagation high temperature synthesis process (reaction synthesis process). According to this process, a mixture of Ti and Al powders is heated to a temperature higher than the reaction temperature so that the reaction is locally initiated. The heat resulting from the local reaction causes a chain reaction which propagates the reaction to the entire mixture so that an intermetallic compound can be obtained without melting the mixture.
It can be surmised that the ratio of the volume occupied by voids in an intermetallic compound or the porosity has a negative effect on the mechanical strength as is the case with other materials. However, the use of Ti-Al intermetallic compounds was started so recently that the relationship between the porosity and the mechanical strength has not been fully determined, and more research is needed for ensuring a high level of reliability in applying Ti-Al intermetallic compounds to various mechanical components by allowing accurate prediction of mechanical strength when the porosity is given.
When a highly dense structure is to be attained in a Ti-Al intermetallic compound, it is necessary to use a high temperature and pressure. It requires expensive special facilities and equipment to achieve such a high temperature and pressure. Furthermore, Ti-Al intermetallic compounds are known to be unsuitable for working. For instance, when a member made of a Ti-Al intermetallic compound is to be forged, an extremely high load is required to carry it out. Therefore, conventionally, it was necessary to conduct special treatments to obtain a fine crystal grain structure (less than 15 .mu.m), and forge the material at a temperature in excess of 1000.degree. C.